1. Field of the Invention
The present invention relates generally to rotary actuators for use in disk drives, and more particularly to an actuator arm assembly having bearing gap formed between bearing outer race and pivot sleeve for mitigating torque ripple on actuator arm in a disk drive.
2. Description of the Prior Art
A typical actuator arm assembly for use in a disk drive includes an actuator arm having an actuator bore disposed therethrough. The actuator arm is configured to pivot about an axis of rotation axially disposed within the actuator bore. A pivot sleeve is disposed within the pivot actuator bore. Within the pivot sleeve is a bearing assembly having an outer bearing race, inner bearing race and bearings balls therebetween. The outer bearing race is secured to the inner surface of the pivot sleeve.
A side screw is often utilized to attach the pivot sleeve to the actuator arm. The side screw tensile force and the compressive force from the contact interface between the actuator bore and pivot sleeve can deform the pivot sleeve. Such deformation of the pivot sleeve may result in deformation or distortion of the attached bearing outer race. High and inconsistent torque ripple is then generated by excessive distortion of the bearing outer race. Torque ripple results in an inconsistency in the amount of torque required to rotate the actuator arm during rotation thereof. Excessive torque ripple can cause error in the servo system and increase access time. The amount of torque ripple may be mitigated by increasing the thickness of the pivot sleeve. However this must be restricted by disk drive design constraints, such as actuator inertia, space about the pivot, servo performance, and drive assembly.
Accordingly, there is a need in the art for an improved actuator arm assembly which reduces excessive torque ripple in comparison to the prior art.
An aspect of the invention can be regarded as an actuator arm assembly for use in a disk drive. The actuator arm assembly includes an actuator arm having an actuator bore disposed therethrough. The actuator arm is configured to pivot about an axis of rotation axially disposed within the actuator bore. The actuator bore has pivot sleeve contact areas. The actuator arm assembly further includes a pivot cartridge concentrically received within the actuator bore. The pivot cartridge includes a pivot sleeve which is formed to exert compressive force radially from the axis of rotation against the actuator bore adjacent the pivot sleeve contact areas. The pivot sleeve is formed to locally deform radially relative to the axis of rotation adjacent the pivot sleeve contact areas. The pivot cartridge further includes a bearing outer race which is concentrically received within and partially concentrically attached to the pivot sleeve. The pivot cartridge further includes a bearing gap formed between the bearing outer race and the pivot sleeve for inhibiting transfer of force between the pivot sleeve and the bearing outer race, thereby mitigating deformation of the bearing outer race in order to mitigate torque ripple on the actuator arm about the axis of rotation.
In an embodiment of the present invention, the actuator arm further has a screw hole generally radially extending toward and perpendicular to the axis of rotation. The actuator arm assembly further includes a screw which is sized and configured to attach the pivot sleeve to the actuator arm. The actuator arm is formed to receive the screw with the screw being axially aligned perpendicular to the axis of rotation. The screw is engaged with the pivot sleeve between the pivot sleeve contact areas of an adjacentmost portion of the actuator bore. In this regard, the actuator bore has an actuator bore notch formed therein between the pivot sleeve contact areas.
In one embodiment, the pivot sleeve contact areas may be disposed about an arc which is less than 180 degrees about the axis of rotation. The pivot sleeve may have a gap portion which is disposed adjacent the bearing gap and an attachment portion which is attached to the bearing outer race. Further, the attachment portion may be adhesively bonded to the outer race. The gap portion is generally defined by an average first radius from the axis of rotation and the attachment portion is generally defined by an average second radius from the axis of rotation, with the average first radius being greater than the average second radius. Further, the pivot sleeve is formed to locally deform radially outward from the axis of rotation between the pivot sleeve contact areas. The pivot sleeve may have two pivot sleeve notches formed thereon adjacent the bearing gap to facilitate local deformation of the pivot sleeve radially outward from the axis of rotation between the pivot sleeve contact areas.
In another embodiment of the actuator arm assembly of the present invention, the pivot sleeve is press fit to and within the actuator bore. The actuator bore may have several pivot sleeve contact areas and the pivot cartridge may have several bearing gaps disposed in radial alignment with respective ones of the pivot sleeve contact areas.